The invention pertains to a side channel blower which is intended to be used, in particular, as a combustion air blower for motor vehicle heaters; such heaters can be designed as air heating devices or water heating devices.
German Pat. No. 31 44 787 and corresponding U.S. Pat. No. 4,456,423 describe a side channel blower of the type mentioned above which has a blower housing in which there is at least one side channel. Right next to the side channel is an impeller which has a number of vanes. The blower housing also has an inlet opening and a discharge opening which are connected to the side channel. Between the inlet side and the delivery side of the blower is a cross piece.
In a side channel blower of this type, the pressure which can be achieved with the side channel blower is proportional to the uncoiled length of the side channel. The circumferential lengths (projected onto the impeller) of the inlet and discharge openings and of the cross piece between the inlet and delivery sides of the blower have then be subtracted from this uncoiled length. The point is that compression is not possible in these areas.
If, as is usually the case, the inlet and discharge openings as well as the cross piece are relatively long in the circumferential direction, then approximately one-third to one-half of the uncoiled length of the side channel cannot be used for the actual compression process. Therefore, the pressure which can be achieved with such a side channel blower is not optimum.
The goal of the invention is thus to increase the outlet delivery pressure which can be achieved with such a side channel blower without increasing the overall dimensions of the side channel blower and/or raising the rpm.
A side channel blower in accordance with preferred embodiments of the invention is excellently suited to accomplishing this goal by virtue of the characteristics that, relative to the plane of a cross piece between the inlet and delivery sides of the blower, the inlet and outlet openings are on axial opposite sides of the blower housing and the inlet opening feeds into the side channel in the circumferential direction of impeller rotation.
In a side channel blower of the type encompased by the invention, the uncoiled side channel length which can be used for compression is increased by virtue of the fact that, the length of the inlet opening, projected onto the impeller and measured in the circumferential direction, is significantly reduced since it is only minimal in the circumferential direction and empties into the side channel in the impeller's direction of rotation. With respect to the plane of the cross piece, the discharge opening is also in an axially opposed position, on the other side of the blower housing relative to the cross piece. The effect of this is that the air which enters via the inlet opening is fed in the circumferential direction to the side channel in a way which promotes flow, thus improving the blower's efficiency, but at the same time the arrangement is fashioned in such a way that in the area of the inlet opening only a very small portion of the side channel's uncoiled length remains unused for the actual compression process. This means, surprisingly enough, an increase in the compression pressure which can be achieved with the side channel blower, without it being necessary to alter the basic dimensions of the blower housing and impeller and/or the impeller's speed.
Additionally, the size of the cross piece as measured in the circumferential direction of the blower housing is minimized since, in the invention's design, it is sufficient for the cross piece to bridge the gap between two successive vanes of the impeller. This minimum size of the cross piece thus amounts approximately to the distance between two successive vanes of the impeller with allowance for the angle ratios between the edges of the cross piece and the edges of the impeller vanes.
The uncoiled side channel length which cannot be used for the actual compression process in the area of the discharge opening is also reduced by having the discharge opening carry off the compressed air in a radial direction to deliver it for the use intended for it. Because of this further reduction in the side channel area which cannot be used for compression, the pressure which can be achieved with the side channel blower can be increased even more.
If the compressed air emerges from the side channel blower discharge opening in the circumferential direction, it is possible to reduce the unusable uncoiled side channel length in the area of the discharge opening as much as possible in order to achieve a higher overall side channel blower delivery pressure. In addition, when the compressed air is carried off in this way, the flow resistance in the area of the discharge opening is extremely slight so that the spiral flow hugs the walls of the side channel and can then be carried off in the impeller's direction of travel with no significant deflection.
If the directions in which both the inlet opening and the discharge opening empty lie in the circumferential direction, then it is advantageous to provide a partition between the delivery and inlet sides of the blower, this partition is designed to provide flow-improving guidance in the area of both the inlet opening and the discharge opening in the axial and/or radial directions.
In order to make sure that there is as little resistance as possible to the inlet and discharge of the air in the side channel blower of the invention, the inlet cross-section of the inlet opening and/or the discharge cross-section of the discharge opening is/are enlarged.
In order to avoid sacrificing some of the usable uncoiled side channel length in the case of the type of enlargement mentioned above, the inlet cross-section of the inlet opening is enlarged in the axial direction of the blower housing, so that while a relatively large volume can be provided via the expanded inlet crosssection of the inlet opening, at the same time there is no need to accept a corresponding reduction in the pressure which can be achieved with the side channel blower. Of course, the discharge opening can be designed in a similar way in the discharge area.
In addition, in a side channel blower having an adjustable bypass opening for regulating the blower output, in accordance with an embodiment of the invention, the bypass opening is placed directly in the wall of the side channel, and in this case, the bypass opening is as far away from both the inlet opening and the discharge opening as possible. This arrangement of the bypass opening simplifies not only the manufacture of a side channel blower of this type, since allowance can be made for this type of opening in the cast section of the blower housing itself, but it has also been found, surprisingly enough, that even when a bypass opening is opened to regulate output, there is a considerably steeper blower characteristic curve than is obtained with the previous designs of bypass controls, so that the upstream and downstream consumers in the overall system have hardly any further effect on the delivery of the blower and the delivery, thus, has a directly proportional relation to the delivery obtained when the bypass opening is closed, almost no matter what the behavior of the consumer is. Since in the case of the design of the side wall blower of the invention the bypass opening is relatively far from the blower discharge opening, in the area between the bypass opening and the blower discharge opening there still exists the possibility that the residual air present in this area in the side channel blower may be further compressed when delivery takes place. This explains, in the case of an open bypass opening, the blower characteristic curve's plot which, as regards steepness, is quite similar to the blower characteristic curve obtained with a closed bypass opening.
It has also been found to be advantageous to arrange the bypass opening in an area extending over one-half to two-thirds of the uncoiled length of the side channel, measured from the inlet opening. In this type of arrangement, approximately one-half to one-third of the length of the side channel is still available for further compression of, for example, the air in the side channel blower up to the discharge opening of the blower even when the bypass opening is open; this means that the blower characteristic curve will have a steeper plot than was the case with the previous bypass control systems. Preferably, the bypass opening is located approximately mid-way between the inlet opening and the discharge opening of the blower.
In order to ensure an adequate adjustment range for output regulation by the bypass opening of the invention, the size of the bypass opening is selected with respect to its location so that its size is inversely proportional to its distance from the blower inlet opening. Since the pressure in the side channel increases as the distance from the blower inlet opening increases, the bypass opening should thus be made larger the closer it is to the inlet opening in order to be able to draw off a large enough quantity of air to regulate the blower output, even when the pressure in the side channel blower is low. The further the bypass opening is from the blower inlet opening, however, the smaller it can be made. Thus, an advantageous compromise can be struck by arranging the bypass opening approximately mid-way between the inlet and discharge openings of the blower. This type of arrangement yields a bypass opening size which can be readily provided and which, in particular, causes no significant impairment of the strength of the blower housing.
In order to ensure that the bypass opening will have as large a clear cross-section as possible, it is given an oblong design.
In order, in the event of an open or even a partly open bypass opening, to guarantee that enough air will discharge via the bypass opening to regulate the system's output, the bypass opening is placed in the side channel wall in such a way that it points directly tangentially to the flow direction of the spiral flow in the side channel; in this case the spiral flow will hug the wall surface of the side channel formed in the blower housing, and with this type of arrangement the spiral flow can then be drawn off with very little resistance.
In accordance with preferred embodiments of a control for adjusting the opening cross-section of the bypass opening, in order to ensure easy access to this adjustment device, this control should be located on the front of the blower housing which faces toward the drive motor and faces away from the delivery output of the blower as well as from the impeller.
In order to keep the overall height for the control at the back of the blower housing as small as possible, a set screw is used as the adjustment control and is arranged parallel to or inclined with respect to the wall surface of the blower housing. Of course, the set screw control can also be arranged normal to this wall surface; this decision will depend on the space available in this area of the heater.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.